Well
Sonic the Hedgehog's titular character was not voiced by a big name star. I didn't know who
Ben Schwartz was before reading his Wikipedia page today, but I don't think it's a name that draws crowds. I find it a bit interesting that both him and Chris Pratt has had regular roles in
Parks and Recreation.
On Pratt's casting: sounds bad. I've only seen his acting in
The Lego Movie and
The Lego Movie: The Second Part, but from descriptions of
Guardians of the Galaxy's lead character and his character on
Parks and Recreation I'd say his forte is portraying characters that would be at home as a shonen manga protagonist. I could see him voicing Monkey D. Luffy, Naruto or Son Goku, since he seems to be portraying lovable dumb-asses a lot. That however is not how I imagine Mario, I imagine Mario as a more mature person. And this is not getting into that Mario often speaks with an Italian accent, something I doubt will be present with Pratt in the role.